Ah, spring 2018. The time that everyone and their moms suddenly decides to start the keto diet to get in shape before summer hits. But there’s something you should know before you hop on the high-fat, low-carb bandwagon: The plan wasn’t actually created to help anyone fit into a smaller pair of shorts.
The ketogenic diet was devleoped in the 1920s to treat…wait for it..epilepsy. Doctors at the Mayo Clinic in Minnesota noticed that some epilepsy patients who were exhibited signs like low blood sugar—or were “starving”—had fewer seizures. So they created a diet meant to trick your body into thinking it’s starving (without the whole not having enough sustenance to live part).
Here’s how it works: Patients follow a meal plan that’s 60-75% fat, 15-30% protein, and 5-10% carbs, which sends their body into a state called ketosis. When they hit this state, their body breaks fat into organic compounds called ketones, which it then uses for energy. And since their bod doesn’t have its first choice for energy—carbs—it kinda-sorta thinks it’s starving.
“Our brains use glucose as its primary energy source,” says Joseph Sirven, M.D., professor of neurology at the Mayo Clinic in Arizona. “With starvation, your body will figure out a way to generate glucose for the brain because the brain needs it at all times.”
So how does this affect seizures? That’s the “million dollar question,” says Sirven, who’s also a fellow at the American Academy of Neurology. As far as scientists know, the ketones seem to have an anti-electrical effect on the brain (either from the chemical properties of the ketones themselves or how they affect the pH levels of the brain). And since seizures are abnormal electric discharges of the brain, that can mean no more seizures.
The diet, when followed extremely strictly, can help epilepsy patients who are difficult to otherwise treat. Because the plan is so extreme, it’s usually prescribed for children, because their parents can control their diets more easily. We adults are limited by our own willpower, because carbs are delicious.
The diet’s use in childhood epilepsy was even chronicled in the 1997 Meryl Streep movie First, Do No Harm, which was based on the true story of the patient Charlie Abrahams; his parents started the Charlie Foundation to spread the word about his success using the ketogenic diet to stop his seizures.
Recently, though, there has been an uptick of interest in the diet—and for reasons that have nothing to do with epilepsy. Some studies have examined its effects on conditions like heart disease and Type 2 diabetes, but there’s not much long-term evidence that the diet helps anything other than seizures. “There’s a lot of claims being made, but there’s not a lot of quality research to support those claims yet,” says Mascha Davis, a registered dietitian and spokeswoman for the Academy of Nutrition and Dietetics.
There are also claims that are far more extreme about the keto diet. For example, Kourtney Kardashian recently raved about her experience on the diet, which she said she started on doctors’ orders to lower levels of mercury and lead in her system. “This is one of those really extreme claims that’s definitely not backed up by any science,” Davis says. “If someone had high levels of mercury in their body, that would be manifesting in a lot of severe ways, and cutting out carbs is not the way to treat that.”
There is strong evidence that the keto diet does result in weight loss, but the reason why is up for debate since there could be several factors at play. But Davis says people who lose weight on the keto diet tend to lose primarily water weight—and once you start eating normally again, the weight will come right back.
Before you dive into the keto diet to shed a few quick pounds, keep in mind that there are some pretty nasty downsides. Common side effects of the keto diet include rapid muscle loss if you’re not eating enough calories, headaches, and nausea (sometimes referred to as the “keto flu”). Plus, you can feel constipated because your diet lacks fiber. And people with diabetes who try the keto diet risk major complications from low blood sugar, Davis says.
Experts have expressed skepticism about the diet’s long-term advantages for weight loss, and Davis agrees—she wouldn’t recommend it to people trying to lose weight. “The people who should be doing this are kids that have epilepsy who, in addition to their physician recommending this, have failed other treatment methods,” she says. “But it’s something that really needs to be done with a medical team involved.”